Page 523 - Practical Well Planning and Drilling Manual

Appendix NEW! revised 11/00/bc 1/30/01 3:30 PM Page 499

[ ]
Glossary

Thermal Decay Time log. Schlumberger wireline tool that analyzes
the decay of fast neutrons to determine formation and borehole sigma
values. Used also for gas detection and discrimination, porosity analy-
sis, reservoir and waterflood monitoring, and through drillpipe for-
mation evaluation.

Thinner. Any of various organic agents (tannins, lignins, lignosul-
fonates, etc.) and inorganic agents (pyrophosphates, tetraphosphates,
etc.) that are added to a drilling fluid to reduce the viscosity and/or
thixotropic properties.

Thixotrophy. The ability of fluid to develop gel strength with time.
The property of a fluid which causes it to build up a rigid or semi-
rigid gel structure if allowed to stand at rest, yet can be returned to a
fluid state by mechanical agitation. This change is reversible.

Titration. A method, or the process of using a standard solution for
the determination of the amount of some substance in another solu-
tion. The known solution is usually added in a definite quantity to
the unknown until a reaction is complete.

Tooljoint or Tool Joint. A drill-pipe coupler consisting of a pin and
box of various designs and sizes. The internal design of tool joints
has an important effect on mud hydrology.

Torque. A measure of the force or effort applied to a shaft causing
it to rotate. On a rotary rig this applies especially to the rotation of
the drill stem in its action against the bore of the hole. Torque reduc-
tion can usually be accomplished by the addition of various drilling
fluid additives.

Total Depth or TD. The greatest maximum depth reached by the
drill bit.

Tour. A person’s turn in an orderly schedule. The word that designates
the shift of a drilling crew is pronounced as if it were spelled t-o-w-e-r.

499